Cantilevered gantry apparatus for x-ray imaging

ABSTRACT

An x-ray scanning imaging apparatus with a rotatably fixed generally O-shaped gantry ring, which is connected on one end of the ring to support structure, such as a mobile cart, ceiling, floor, wall, or patient table, in a cantilevered fashion. The circular gantry housing remains rotatably fixed and carries an x-ray image-scanning device that can be rotated inside the gantry around the object being imaged either continuously or in a step-wise fashion. The ring can be connected rigidly to the support, or can be connected to the support via a ring positioning unit that is able to translate or tilt the gantry relative to the support on one or more axes. Multiple other embodiments exist in which the gantry housing is connected on one end only to the floor, wall, or ceiling. The x-ray device is particularly useful for two-dimensional multi-planar x-ray imaging and/or three-dimensional computed tomography (CT) imaging applications.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/354,563, filed Feb. 14, 2006, which is a continuation of U.S.application Ser. No. 10/459,405, filed Jun. 11, 2003, now U.S. Pat. No.7,001,045, which claims the benefit of U.S. Provisional Application No.60/388,063, filed Jun. 11, 2002, the entire teachings of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

Healthcare practices have shown the tremendous value ofthree-dimensional imaging, mainly as a diagnostic tool in the RadiologyDepartment. Other areas of care, including the operating room, intensivecare departments and emergency departments, rely on two-dimensionalimaging (fluoroscopy, ultrasound, 2-D mobile X-ray) as the primary meansof diagnosis and therapeutic guidance. This is mainly due to the cost,size, and expertise required to operate traditional three-dimensionaldevices. Moreover, radiologic quality CT scanners have been designed tomaximize image quality at the expense of mobility. Truly practical andmobile imaging solutions for “non-radiology departments” capable ofperforming both 2D and 3D imaging in the same device have yet to bedeveloped. Previous attempts simply do not address the true need, whichis to maintain a sizable volume while meeting a level of expected imagequality. In the past, there have been two types of devices proposed toaddress this need. One type of device uses a mobile C-arm and spins itaround the anatomy, such as the Siremobil Iso-C3D system from SiemensAG. These C-arm based attempts have a limited field of view, areprocedurally cumbersome and have an inherent limit to the image quality.

Others have attempted to make a fixed-bore CT mobile, such as the devicedescribed in Butler W. E. et al, A Mobile CT Scanner with Intraoperativeand ICU Application, 1998.(http://neurosurgery.mgh.harvard.edu/mobileCT.htm). However, theseso-called “mobile CT scanners” are characterized by the elevated dosinglevel of a traditional fixed CT scanner, they are difficult to maneuver,and they are incapable of performing 2D imaging when that is all that isneeded.

In general, the fluoroscopic C-arm attempts meet the criteria ofmobility and flexibility, but fall short on image quality and imagevolume. The “mobile CT scanner” attempts meet the criteria of imagevolume and quality, but fail to address the practical issues ofusability and cost. Additionally, state of the art CT scanners areincapable of translating and tilting in the same fashion of mobilefluoroscopy systems.

A truly mobile and practical solution for ‘non-radiology department’ 3-Dimaging also capable of performing 2D imaging does not yet exist. Thisis mainly due to the fact that current tomographic scanners are notmobile in a practical manner. The inability to move a CT scanner withthe same degrees of freedom of mobile C-arms has hindered the acceptanceand use of mobile three-dimensional imaging. This has limited the valueof three-dimensional computed tomographic imaging to areas mainly as adiagnostic tool in the Radiology Department.

There is a need for a mobile CT scanner for use in the operating room,intensive care unit, emergency room and other parts of the hospital, inambulatory surgery centers, physician offices, and the militarybattlefield, which is truly mobile and capable of performing both 2D and3D x-ray imaging.

SUMMARY OF THE INVENTION

The present invention is directed to an imaging apparatus comprising agenerally O-shaped gantry ring having an x-ray source and a detector.The gantry ring is rigidly or movably secured on one side of the ring toa support structure, such as a mobile cart, a wall, a ceiling, a floor,or a patient table, in a cantilevered fashion.

According to one aspect, a positioner assembly can secure the gantryring to the support structure in a cantilevered fashion, the positionerassembly permitting the gantry to translate in at least one direction,and/or rotate around at least one axis, relative to the supportstructure.

According to one aspect, the x-ray source is contained inside the gantryring, opposed to a detector array. The x-ray source (and optionally thedetector) can rotate around the inside of the gantry ring, preferablythrough a full or partial 360 degree scan around the interior of thegantry. The imaging apparatus is particularly advantageous for medicalimaging applications, including 3D computerized tomographic (CT) imagingand 2D x-ray radiographic scanning, as well as other medical,scientific, and industrial applications.

According to another aspect, a method for imaging an object with animaging system having a substantially O-shaped gantry secured to asupport structure in a cantilevered fashion by a ring positioning unit,comprises positioning the object within a central opening of thegenerally O-shaped gantry; operating the ring positioning unit toposition the gantry at a predetermined position and orientation relativeto the support structure; and obtaining an image of the object.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a schematic diagram of a mobile x-ray scanning system with acantilevered O-shaped gantry according to one embodiment of theinvention;

FIG. 2 shows the scanning system of FIG. 1 with the cantileveredO-shaped gantry in a translated and tilted position via a ringpositioning unit;

FIG. 3 shows a gantry ring positioning unit for translating a gantry inthree directions and tilting the gantry with respect to one axis,according to one aspect of the invention;

FIG. 4 shows a ring positioning unit for translating the gantry ring inan in/out direction;

FIG. 5 shows a ring positioning unit for translating the gantry in avertical direction;

FIG. 6 shows a ring positioning unit for translating the gantry in alateral direction;

FIG. 7 shows a ring positioning unit for tilting the gantry with respectto one axis;

FIG. 8 shows a floor-mounted cantilevered gantry ring with ringpositioning unit;

FIG. 9 shows a wall-mounted cantilevered gantry ring with ringpositioning unit; and

FIG. 10 shows a ceiling-mounted cantilevered gantry ring with ringpositioning unit.

DETAILED DESCRIPTION OF THE INVENTION

A description of preferred embodiments of the invention follows.

FIG. 1 is a schematic diagram showing an x-ray scanning system 10 inaccordance with one embodiment of the invention. The x-ray scanningsystem 10 includes a gantry 11 secured to a support structure, whichcould be a mobile or stationary cart, a patient table, a wall, a floor,or a ceiling. As shown in FIG. 1, the gantry 11 is secured to a mobilecart 12 in a cantilevered fashion via a ring positioning unit 20. Asdescribed in further detail below, the ring positioning unit 20 cantranslate and/or tilt the gantry 11 with respect to the supportstructure to position the gantry 11 in any number of imaging positionsand orientations.

The mobile cart 12 of FIG. 1 can optionally include a power supply, anx-ray power generator, and a computer system for controlling operationof the x-ray scanning device and for performing image processing,storage of x-ray images, or other data processing functions. In apreferred embodiment, the computer system controls the positioning unit20 to enable the gantry 11 to be quickly moved to a particularuser-defined position and orientation. The computer preferably has amemory that is capable of storing positioning information relating toparticular gantry positions and/or orientations. This stored positioninginformation can be used to automatically move the gantry to apre-defined configuration upon demand.

The mobile cart 12 preferably also includes a display system 60, such asa flat panel display, for displaying images obtained by the x-rayscanner. The display can also include a user interface function, such asa touch-screen controller, that enables a user to interact with andcontrol the functions of the scanning system. In certain embodiments, auser-controlled pendant or foot pedal can control the functions of thescanning system.

It will be understood that one or more fixed units can also perform anyof the functions of the mobile cart 12.

According to one aspect, the x-ray scanning system of the invention canbe used to obtain two-dimensional planar or three-dimensionalcomputerized tomographic (CT) x-ray images of an object, such as apatient. In the embodiment shown in FIG. 1, the gantry 11 is a generallycircular, or “O-shaped,” housing having a central opening into which anobject being imaged is placed. The gantry 11 contains an x-ray source 13(such as a rotating anode pulsed x-ray source) that projects a beam ofx-ray radiation 15 into the central opening of the gantry, through theobject being imaged, and onto a detector array 14 (such as a flat paneldigital detector array) located on the opposite side of the gantry. Thex-rays received at the detector 14 can then be used to produce atwo-dimensional or three-dimensional image of the object usingwell-known techniques.

The x-ray source 13 is able to rotate around the interior of the gantry11 in a continuous or step-wise manner so that the x-ray beam can beprojected through the object, and through a common isocenter, at variousangles over a partial or full 360 degree rotation. The detector array isalso rotated around the interior of the gantry, in coordination with therotation of the x-ray source, so that for each projection angle of thex-ray source, the detector array is positioned opposite the x-ray sourceon the gantry. The apparatus is thus able to obtain high-quality x-rayimages of the targeted object in any projection plane over a partial orfull 360 degree rotation.

FIG. 2 shows the scanning system of FIG. 1 with the cantileveredO-shaped gantry 11 in a translated and tilted position via a ringpositioning unit 20. The positioning unit 20 connects to the gantry 12on one side, securing the gantry to the a mobile cart 12 or othersupport in a cantilevered fashion. The positioning unit 20 enables thegantry 11 to translate and/or rotate with respect to the supportstructure, including, for example, translational movement along at leastone of the x-, y-, and z-axes, and/or rotation around at least one ofthe x- and y-axes. As shown in FIG. 2, the positioner 20 is capable oftranslating the gantry 11 in three directions relative to the cart 12,including a vertical direction (i.e. up and down), an in/out direction(i.e. towards and away from the cart), and a lateral direction (i.e.along the rotational axis of the x-ray source). The positioner is alsocapable of tilting the gantry around one or more axes. It will beunderstood that various other embodiments of the invention exist wherethe cantilevered gantry remains fixed relative to the support structure,or where the gantry is capable of translational or tilting movement incertain directions, but not in others.

The gantry positioning unit 20 can be controlled manually, or, in apreferred embodiment, it is a motorized system that can be movedelectro-mechanically to a desired position. A computerized motioncontrol system can be attached to motorized components of the positionerand one or more discreet positions and orientations of the gantry may bestored in the computer's memory. During operation of the x-ray scanner,pre-defined gantry positions and orientations may be returned to quicklyand easily.

FIG. 3 shows a schematic diagram of the assembled components of a ringpositioning unit 20 in accordance with one embodiment of the invention.Relative motion of the gantry ring is achieved by a set of individualpositioners, including an in/out positioner 305, a vertical positioner307, a lateral positioner 309, and a tilt positioner 311. A Z-bracket313 is used to rigidly connect the vertical 307, lateral 309, and tilt311 positioners to the in/out positioner 305.

Referring now to FIG. 4, the in/out positioner 305 comprises a motorizedassembly for translating the cantilevered gantry ring towards or awayfrom the support structure. The in/out positioner includes a top plate315 upon which the Z-bracket 313 (see FIG. 3) is bolted. The top plate315 is movable along the length of a base plate 317 via blocks 319 whichmate with linear guide rails 321 on the base plate 317. A geared servomotor 323 is rigidly attached to the base plate 317 by a motor mount325. A ball screw 327 is mounted in ball screw mount 329, and runs alongthe length of the base plate 317 parallel to linear guide rails 321. Theball screw 327 is mated with a ball screw nut 333 that is fixedlysecured to the top plate 315. The motor 323 rotates the ball screw 327in a clockwise or counterclockwise direction via motor shaft coupling331. The rotation of the ball screw 327, in either a clockwise orcounterclockwise direction, causes the ball screw nut 333, and thus thetop plate 315, to travel up and down the length of the ball screw 327.The linear guide and blocks steer the top plate as it is displaced alongthe length of the base plate 317 by servo motor 323. In this way, thecantilevered gantry assembly can be translated towards or away from thesupport structure, such as a mobile cart, floor, wall, ceiling, or apatient table, in a controlled manner.

FIG. 5 shows the vertical positioner 307 for translating the generallyO-shaped cantilevered gantry vertically relative to the supportstructure. In the embodiment shown in FIG. 5, the vertical positioner307 is a motorized assembly that is essentially identical to the in/outpositioner 305 in terms of its structure and operation. However, thevertical positioner 307 is oriented vertically so that the top plate canbe translated upwards or downwards relative to the base plate. Asillustrated in FIG. 5, the vertical positioner includes a top plate 315movably mounted onto a base plate 317 via blocks 319 which ride onlinear guide rails 321. The top plate 315 is translated relative to thebase plate 317 by a servo motor 323 and ball screw 327, as described inconnection with FIG. 4. As shown in FIG. 3, the top plate of thevertical positioner 307 is rigidly secured to the Z-bracket 313, and theentire Z-bracket assembly is secured to the top plate of the in/outpositioner 305. The top plate of the vertical positioner 307 thusremains vertically fixed to Z-bracket, while the base plate of thevertical positioner 307 is capable of translating vertically up and downin a telescoping fashion relative to the Z-bracket and the in/outpositioner.

FIG. 6 shows the lateral positioner 309 for translating the generallyO-shaped cantilevered gantry in a lateral direction relative to thesupport structure. In this embodiment, the lateral positioner 309comprises a motorized assembly that is essentially identical to thepreviously-described in/out positioner 305 and vertical positioner 307in terms of its structure and operation. However, the lateral positioner309 is oriented in a lateral direction so that the top plate can betranslated from side to side relative to the base plate. As illustratedin FIG. 6, the lateral positioner includes a top plate 315 movablymounted onto a base plate 317 via blocks 319 which ride on linear guiderails 321. The top plate 315 is translated relative to the base plate317 by a servo motor 323 and ball screw 327, as described in connectionwith FIG. 4. As shown in FIG. 3, the base plate of the lateralpositioner 309 is rigidly attached to the base plate of the verticalpositioner 307. The entire lateral positioner 309 is thus translatedin/out or vertically up/down with the respective movements of the in/outpositioner 305 and the vertical positioner 307. The top plate of thelateral positioner 309 can be attached to the gantry ring to translatethe ring laterally left and right relative to the Z-bracket 313 and thesupport structure.

FIG. 7 shows the tilt positioner 311 for tilting the generally O-shapedcantilevered gantry relative to the support structure. An inner ring 335includes mounting holes 337 for rigidly attaching the ring to the topplate of the lateral positioner 309. An outer ring 339, larger indiameter than the inner ring 335 includes mounting holes 341 for rigidlyattaching the outer ring 339 to the gantry 11. The outer ring 339includes a gear with external teeth and is rotatable relative to theinner ring 335 on bearings. The complete two-ring assembly is referredto as a slew ring gear 345. A geared servo motor 347, mounted to thelateral positioner 309 by motor mount 349, rotates the slew ring gear345 via a pinion gear 351 with external teeth and a synchronous belt353. Rotation of the slew ring gear tilts the cantilevered gantryrelative to the lateral positioner, as illustrated in FIG. 2. It will beunderstood that a tilt positioner such as described in connection withFIG. 7 can be employed to tilt the gantry about any suitable axis. Forexample, a tilt positioner could be used to join the top plate 315 ofthe in/out positioner 305 to the Z-bracket to permit the gantry torotate about the vertical axis.

According to one aspect, each of the positioner assemblies 305, 307,309, 311 comprising the ring positioning unit 20, includes a mechanismfor providing position feedback information to its respective servomotorin order to enable precise positioning of the gantry along each degreeof translational or rotational motion. For example, referring to FIG. 4,a linear encoder tape can be affixed to a linear guide rail 321 of thebase plate 317, and a read head can be located on a the top plate 315for reading the encoder tape and providing feedback data indicative ofthe relative positions of the top plate 315 and the base plate 317.Similarly, in reference to FIG. 7, a rotary encoder can be used todetermine the relative angular positions of the inner 335 and outer 339rings of the slew ring gear 345. Preferably, the position feedbackmechanism is an absolute position encoder system, so that, at any giventime, a computerized motion control system can precisely determine thetranslational and/or rotational position of the ring positioning unit inall degrees of freedom, and can thus determine the position andorientation of the gantry in three-dimensional space.

Turning now to FIGS. 8-10, various embodiments of a cantileveredO-shaped gantry 11 and ring positioning unit 20 are shown. In FIG. 8,the ring positioning unit 20 is mounted to the floor 355 by the baseplate of in/out positioner. The tilt positioner 311 is mounted to oneside of the gantry 11. This allows the cantilevered gantry to translateand tilt relative to the fixed room.

FIG. 9 shows the ring positioning unit 20 mounted on one side to a wall357, and on the other side to the gantry 11, thus allowing thecantilevered gantry to translate and tilt relative to the fixed room. InFIG. 10, the ring positioning unit 20 is fixed on one side to theceiling 359, and on the other side to the gantry 11. The ringpositioning unit 20 and gantry 11 could be similarly mounted to anysuitable support structure, such as to a table upon which a patientunder examination is placed.

The x-ray imaging systems and methods described herein may beadvantageously used for two-dimensional and/or three-dimensional x-rayscanning. Individual two-dimensional projections from set angles alongthe gantry rotation can be viewed, or multiple projections collectedthroughout a partial or full rotation may be reconstructed using cone orfan beam tomographic reconstruction techniques. This invention could beused for acquiring multi-planar x-ray images in a quasi-simultaneousmanner, such as described in commonly-owned U.S. patent application Ser.No. 10/389,268, filed on Mar. 13, 2003, now U.S. Pat. No. 7,188,998, theentire teachings of which are incorporated herein by reference.

The detector arrays of the present invention include two-dimensionalflat panel solid-state detector arrays. It will be understood, however,that various detectors and detector arrays can be used in thisinvention, including any detector configurations used in typicaldiagnostic fan-beam or cone-beam imaging systems, such as C-armfluoroscopes, or single-sliced or multi-sliced CT scanners, or mobileand fixed-room floroscopy devices which utilize image intensifiertechnology. A preferred detector is a two-dimensional thin-filmtransistor x-ray detector using scintillator amorphous-silicontechnology.

For large field-of-view imaging, the detector array can be translatedto, and acquire imaging data at, two or more positions along a line orarc opposite the x-ray source, such as via a motorized detector rail andbearing system. Examples of such detector systems, and associated beampositioning systems, are described in commonly owned U.S. patentapplication Ser. No. 10/392,365, filed Mar. 18, 2003, now U.S. Pat. No.7,108,421, the entire teachings of which are incorporated herein byreference.

In yet another aspect, the O-shaped gantry can include a segment that atleast partially detaches from the gantry ring to provide an opening or“break” in the gantry ring through which the object to be imaged mayenter and exit the central imaging area of the gantry ring in a radialdirection. An advantage of this type of device is the ability tomanipulate the x-ray gantry around the target object, such as a patient,and then close the gantry around the object, causing minimal disruptionto the object, in order to perform x-ray imaging. Examples of“breakable” gantry devices for x-ray imaging are described incommonly-owned U.S. patent application Ser. No. 10/319,407, filed Dec.12, 2002, now U.S. Pat. No. 6,940,941, the entire teachings of which areincorporated herein by reference.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims. For instance, although theparticular embodiments shown and described herein relate in general tox-ray imaging applications, it will further be understood that theprinciples of the present invention may also be extended to othermedical and non-medical imaging applications, including, for example,magnetic resonance imaging (MRI), positron emission tomography (PET),single photon emission computed tomography (SPECT), ultrasound imaging,and photographic imaging.

Also, while the embodiments shown and described here relate in generalto medical imaging, it will be understood that the invention may be usedfor numerous other applications, including industrial applications, suchas testing and analysis of materials, inspection of containers, andimaging of large objects.

While this invention has been particularly shown and described withreferences to example embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. An imaging apparatus comprising: a generally O-shaped gantry ring; asupport structure; and a ring positioning unit that secures the gantryring to the support structure in a cantilevered manner, and positionsthe gantry ring relative to the support structure.